It is now well established in the scientific community that electromagnetic waves with varying frequencies irradiated by various devices may be hazardous to human health. In some cases, such electromagnetic waves in mega- and giag-hertz range may be the main culprit, whereas the 60-hertz electromagnetic waves may be the main health concern in other cases. It cannot be too emphasized that it is very difficult to shield against magnetic waves of the 60-hertz electromagnetic waves which have wavelengths amounting to thousands of kilometers and that such 60-hertz magnetic waves are omnipresent in any corner of the current civilization.
However, intensity of such electromagnetic waves typically decreases inversely proportional to a square of a distance from a source of such waves to a target. Accordingly, potentially adverse effects from such electromagnetic waves may be minimized by maintaining a safe distance from such a source. Some electrical devices, however, are intended to be used in a close proximity to an user, where typical examples of such devices are hair dryers, hair curlers, electric mattresses or blankets, heating pads, and the like. Accordingly, the Applicant have disclosed numerous electromagnetically-shielded embodiments of such devices.
In contrary to the above devices, conventional electric speakers operate with electric currents having amplitudes lot less than those flowing in such devices. However, certain speakers included in earphones, headphones, cellular phones, and handsets of regular phones are to be disposed close to an ear of an user. Accordingly, although these speakers may emit the electromagnetic waves having less amplitudes, such speakers tend to irradiate the electromagnetic waves directly to brain cells in a close proximity thereto. In particular, the earphones are to be disposed into an ear canal of the ear so that the electromagnetic waves irradiated therefrom may reach the brain cells at a less distance and, therefore, with greater strengths. It is appreciated that the irradiation of such undesirable waves may not be prevented by operating the speakers by a DC current, for such speakers generate the sounds through fluctuating electric currents which inevitably irradiate such electromagnetic waves.
Electromagnetic waves have been proved to affect physiological activities of brain cells. For example, U.S. Pat. Nos. 4,940,453, 5,047,005, 5,061,234, 5,066,272, and 5,267,938 describe various apparatus and methods for stimulating the brain cells by impinging thereto electromagnetic waves. In more recent disclosures, both of U.S. Pat. No. 6,849,040 B2 issued to J. Ruohonen et al. on Feb. 1, 2005 and U.S. Pat. Appl. Pub. No. 2003/0073899 A1 of the same inventors published on Apr. 17, 2003 disclose dose-computing apparatus and method for determining effects of magnetic stimulation on human brain. However, the prior art does not provide any speakers capable of reducing irradiation of the harmful electromagnetic waves to the brain cells of the user.
For example, U.S. Pat. No. 6,590,539 B2 issued to H. Shinichi on Jul. 8, 2003 and another U.S. Pat. Appl. Pub. No. 2002/0060645 A1 of the same inventor published on May 23, 2002 describe dipole antennas of portable communication devices capable of reducing specific absorption rate or “SAR” of electromagnetic waves (to be abbreviated as “EM waves” hereinafter) emitted by such devices. U.S. Pat. No. 6,377,827 B1 issued to N. Rydbeck on Apr. 23, 2002 describes mobile communication devices with foldable antennas which may be disposed away from users during use to reduce the EM waves propagating to the brains of the users, while U.S. Pat. No. 6,246,374 B1 issued to A. Perrotta et al. on Jun. 12, 2001 discloses antenna assemblies of mobile communication devices with main and parasitic antennas disposed away from the users for reducing the EM waves during use. In addition, U.S. Pat. No. 5,586,168 issued to B. Bucalo et al. on Dec. 17, 1996 similarly discloses multi-piece cellular communication devices including antennas disposed toward and away from the rest of such devices and reducing such EM waves emitted thereby. Although these prior art devices may reduce a portion of such EM waves, they fail to reduce the EM waves irradiated to the user from their speakers.
In another class of examples, U.S. Pat. No. 6,418,273 B1 issued to J. Lubinski et al. on Jul. 9, 2002 describes portable CD player devices incorporating less semiconductor devices and minimizing irradiation of the EM waves, while U.S. Pat. No. 6,195,562 B1 issued to R. Pirhonen et al. on Feb. 27, 2001 discloses mobile communication devices capable of restricting maximum transmitting power thereof, thereby limiting power of their EM waves radiated thereby. U.S. Pat. No. 5,777,261 issued to J. Katz on Jul. 7, 1998 discloses mobile communication devices having cases capable of attenuating and diverting their EM waves irradiated thereby, and U.S. Pat. Appl. Pub. No. 2004/0170086 A1 of Y. Mayer et al. published on Sep. 2, 2004 describes microphone devices which may not employ any membranes. U.S. Pat. Appl. Pub. No. 2003/0002691 A1 of H. Ono et al. published on Jan. 2, 2003 describes earphones for portable communication devices capable of being attached thereto at distances and reducing irradiation of the EM waves, while U.S. Pat. Appl. Pub. No. 2002/0098862 A1 of E. Engstrom published on Jul. 25, 2002 describes mobile communication devices with speakers and antennas disposed away from heads of users for reducing exposure of the users to the EM waves from the speakers and antennas thereof. In addition, U.S. Pat. Appl. Pub. No. 2001/0034253 A1 of S. Ruschin published on Oct. 25, 2001 describes mobile communication devices with speakers and microphones coupled by optical paths for reducing radiation of EM waves. Although some of these prior art devices have recognized potential hazards from their speakers, none of the prior art devices teach how to reduce the irradiation of the EM waves from the speakers of such devices.
The prior art also discloses various acoustic paths capable of delivering sounds therethrough. Thus, U.S. Pat. No. 6,825,810 B2 issued to G. Ragner et al. on Nov. 30, 2004 and U.S. Pat. Appl. Pub. No. 2003/0132884 A1 of the same inventors published on Jul. 17, 2003 describe various mobile communication devices employing air channels to route sounds from their speakers to their earpieces, while U.S. Pat. No. 6,631,279 B2 issued to A. Rivera on Oct. 7, 2003 and U.S. Pat. Appl. Pub. No. 2002/0055374 A1 by the same inventor published on May 9, 2002 disclose assemblies of speakers and microphones of cellular communication devices including air tubes for transmitting and receiving acoustic waves for reducing irradiation of the EM waves generated thereby. U.S. Pat. No. 6,377,824 B1 issued to R. Ingbir et al. on Apr. 23, 2002 describes assemblies for cellular communication devices capable of converting electrical signals to acoustic signals to reduce the irradiation of the EM waves, while U.S. Pat. No. 6,181,801 B1 issued to S. Puthuff et al. on Jan. 30, 2001 describes earpieces of mobile communication devices disposed away therefrom through connectors to reduce exposure to the EM waves emitted thereby. In addition, U.S. Pat. Appl. Pub. No. 2004/0125979 A1 of J. Elidan et al. published on Jul. 1, 2004 discloses portable communication devices including tubes for transmitting acoustic waves to and from speakers and microphones and reducing the irradiation of the EM waves, while U.S. Pat. Appl. Pub. No. 2002/0048385 A1 of I. Rosenberg published on Apr. 25, 2002 describes cellular communication devices having assemblies of speakers and microphones coupled by air tubes and receiving and transmitting acoustic waves through the tubes for reducing the irradiation of the EM waves. Though these devices may reduce the exposure of the user to the EM waves, such may be achieved by increasing distances between the user and sources of the EM waves, not by decreasing amounts of the EM waves generated by such devices. In addition, incorporation of such air channels not only introduces mechanical noises to the sounds but also mandates use of additional components such as the air channels.
Various shields have also been described in the prior art so as to shield the user from the EM waves. For example, U.S. Pat. No. 6,855,883 B1 issued to H. Matsui on Feb. 15, 2005 describes shielding materials of electrically conductive fibers woven into a web and incorporated into a case of mobile communication devices, while U.S. Pat. No. 6,708,047 B1 issued to J. Miller et al. on Mar. 16, 2004 discloses annular radiation shields disposed around antennas of mobile communication devices. U.S. Pat. No. 6,314,277 B1 issued to Y-F Hsu et al. on Nov. 6, 2001 discloses radiation shields disposed on one side of an antenna of a mobile communication device for absorbing such EM waves, whereas U.S. Pat. No. 6,184,835 B1 issued to C. Chen et al. on Feb. 6, 2001 describes shielding covers for mobile communication devices for absorbing the EM waves radiated from their antennas. U.S. Pat. No. 6,137,998 issued to H. Holshouser et al. on Oct. 24, 2000 also discloses shields for antennas of cellular communication devices for reducing the EM waves radiated to their users, while U.S. Pat. No. 5,657,386 issued to J. Schwanke on Aug. 12, 1997 describes cellular communication devices including shields incorporated into their cases and absorbing or dispersing such EM waves. U.S. Pat. No. 5,406,038 issued to D. Reiff et al. on Apr. 11, 1995 describes speakers with diaphragms coated with metal layers to prevent transmission of the EM waves therethrough, while U.S. Pat. Appl. Pub. No. 2004/0219328 A1 of K. Tasaki et al. published on Nov. 4, 2004 discloses laminates of soft magnetic materials and insulators capable of being used as countermeasures against a specific absorption rate. In addition, U.S. Pat. Appl. Pub. No. 2004/0090385 A1 of R. Green published on May 13, 2004 describes cellular communication devices with shielding and reflecting layers for reflecting the EM waves away from users, U.S. Pat. Appl. Pub. No. 2002/0137473 A1 of D. Jenkins published on Sep., 26, 2002 discloses shields disposed over speakers of mobile communication devices and obstructing the EM waves irradiated by their speakers, and U.S. Pat. Appl. Pub. No. 2002/0097189 A1 of S. Coloney published on Jul. 25, 2002 describes mobile communication devices with shields which are disposed over speakers and antennas of the devices for reducing the EM waves emitted thereby. Although these shields claim to shield the user from the harmful EM waves, such shields may amount only to electric shields capable of shielding electric waves of the EM waves and may not at all shield magnetic waves of the EM waves.
Therefore, there is a need for electromagnetically-shielded speaker systems which effectively reduce the irradiation of the EM waves from their speakers without affecting the sounds. There also is a need for the speaker systems employing simple countermeasures capable of canceling at least a substantial portion of the EM waves irradiated thereby without compromising their performances and without complicating their configurations. In addition, there is a need for electric and magnetic shields for such speaker systems capable of shielding users from the electric and magnetic waves of the EM waves. There further is a need for speaker systems incorporating multiple mechanisms to shield the users from the EM waves irradiated by their speakers.